In optical scanning systems and the like for recording images on film sheets, the film is often supplied from cassettes. Typically, for such applications as facsimile recording for use in making newspaper printing plates, the film is supplied as a continuous wide sheet, and the cassettes, when fully loaded, have substantial weight. Film is withdrawn as needed, cut to the desired length and placed upon a platen where it is exposed by a traveling scanning beam modulated with the image(s) to be recorded on the film.
Automatic film transport mechanisms were not included in early scanning systems. The early scanning systems were facsimile systems that utilized scanners for reading an image and drum recorders for recording the image. Typically, at the transmitting site, an operator was required to load each original page individually on the scanner while, at the receiving site, an operator loaded each film sheet on the drum recorder individually. At the conclusion of scanning of each original page, the recorded pages were removed from the equipment manually. A disadvantage of such systems was the delay between transmissions occasioned by the manual loading and unloading of originals and film.
In the 1970's flatbed recorders were introduced having an on-line film processor and an automated feed mechanism. The automated feed mechanisms on the receiving equipment reduced the labor requirements over prior systems. Typically, film was extracted from a cassette and loaded into the optical scanning system in time sequence. The film sheet for the next page was not extracted or transported until imaging of the prior film sheet was completed.
In applications such as the newspaper industry it is important to minimize the time allocated between transmissions for loading and unloading film.
Some systems have included only a single cassette of film. If the cassette does not hold enough film for an entire series of transmissions, an additional delay occurs while the cassette is changed. More recently, the approach has been to use two cassettes supported on movable holders which can be activated to bring the needed cassette into position where film can be extracted. The disadvantage of this approach is that it requires rather powerful mechanisms for transporting the heavy cassettes from one position to the next.